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IC 9047 



Bureau of Mines Information Circular/1985 




NOV 27 i9C: 

, OOPY_.. ^,.<$'' 



Lightweight Fiberglass Feed Leg 
for Hand-Held Pneumatic 
Percussion Rock Drills 



By Ellsworth R. Spencer 




UNITED STATES DEPARTMENT OF THE INTERIOR 



T5J 

AMINES 75TH A^»^ 



■tt iaiafMgaCT? ff*ptU- 



Information Circular 9047 



Lightweight Fiberglass Feed Leg 
for Hand-Held Pneumatic 
Percussion Rock Drills 



By Ellsworth R. Spencer 




UNITED STATES DEPARTMENT OF THE INTERIOR 

Donald Paul Model, Secretary 

BUREAU OF MINES 
Robert C. Norton, Director 






Library of Congress Cataloging in Publication Data: 



Spencer, Ell 


s worth R 












Lightweigh 
rock drills. 


fiberglass 


feed 


leg for hand-held 


pneumatic percussion 


(Informatior 
reau of Mines ; 


1 circular / 
9047) 


Unite 


d States Department of the 


Interior, 


Bu- 


Supt. of Docs, no.: I 28.27: 


9047. 








1. Rock drills. 2. Boring — Equipment and supplies. 
Series: Information circular (United States. Bureau of Mines 


I. Title. 
) : 9047. 


ll. 


^mm^^xiA^ 


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CONTENTS 

Page 



k 



y Abs tract i 1 

Introduction 2 

\'^ Rationale 2 

^ Design 3 

-^ Testing 5 

Summary 6 

ILLUSTRATIONS 

1. Standard aluminum feed leg on hand-held percussion drill 3 

2 . Components of fiberglass feed leg 4 

3. Overall dimensions of fiberglass feed leg 4 

4. Offset stoper version of fiberglass feed leg 5 

5 . Standard version of fiberglass feed leg 5 

TABLES 

1 . Comparisons of rock-drill and feed-leg weights 3 

2. Approximate costs of feed legs 3 











UNIT OF MEASURE ABBREVIATIONS 


USED IN 


THIS REPORT 


dBA 


decibel (A-weighted network) 


Ibf 


pound (force) 


fflbf 


foot pound (force) 


pet 


percent 


in 


inch 


psi 


pound per square inch 


lb 


pound (mass) 







LIGHTWEIGHT FIBERGLASS FEED LEG FOR HAND-HELD 
PNEUMATIC PERCUSSION ROCK DRILLS 

By Ellsworth R. Spencer^ 



ABSTRACT 

A lightweight fiberglass feed leg for hand-held pneumatic percussion 
rock drills has been fabricated and tested by the Bureau of Mines. Its 
lighter weight facilitates easier handling of the rock drill apparatus, 
thereby reducing the potential for back injury to the driller and in- 
creasing drilling productivity. Current hand-held feed leg drills of 
the same class are 50 pet heavier than the Bureau-devised feed leg 
drill, which is comprised of a reduced-noise drill and the fiberglass 
feed leg. In-mine tests of the fiberglass leg showed that its perform- 
ance and cost are comparable to those of standard aluminum feed legs. 



1 
Physical scientist, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 



INTRODUCTION 



Hand-held pneumatic percussion rock 
drills, called "stopers" (for vertical 
holes) or "feed leg drills" (for hori- 
zontal or angled holes) are thrust into 
the rock by means of an air-powered cyl- 
inder called a "feed leg" (fig. 1). 
They are heavy (over 100 lb), bulky, and 
must be set up and operated by hand. 
Basically, a feed leg consists of two 
tubes, an outer tube usually made of 
aluminum for lightness and an inner tube 
made of aluminum or steel that is con- 
nected to the underside of the rock 
drill. The inner tube is fitted with a 
piston at its lower end that slides in- 
side the outer tube when air pressure is 
applied. At the bottom of the outer 
tube is the stinger, a steel point that 
digs into the ground for support of the 



feed leg and rock drill. A steel bushing 
fitted to the top end of the outer tube 
guides the inner tube when it is extend- 
ed. Pressurized air is passed through 
the center of the inner tube and piston 
and forces them to slide forward, therby 
providing thrust to the drill. 

The feed leg provides vertical and hor- 
izontal thrust while the drill operator 
provides the needed directional thrust. 
During drilling, the weight of the rock 
drill must be balanced between the forces 
being exerted by the feed leg and the 
driller; otherwise, the drill will "hang" 
on the steel. As the hole gets deeper, 
the inner tube slides out until it is 
fully extended. More drill steel is then 
added, or the inner tube is retracted and 
the feed leg repositioned, or both. 



RATIONALE 



Although standard aluminum and steel 
feed legs do not present serious health 
and/or safety problems by themselves, 
they have received attention from the Bu- 
reau of Mines because they are used on 
hand-held mining drills, which do present 
such problems. Noise is the greatest 
health hazard associated with these 
drills; noise levels of standard drills 
commonly range from 115 to 120 dBA or 
greater. Because Federal regulations do 
not permit continuous noise levels above 
115 dBA, the mere startup of these drills 
can result in operator overexposure. In 
addition, the excessive vibration of the 
drill handle can lead to Raynaud's 
("white finger") disease, an affliction 
characterized by severe damage to ar- 
teries and tissues of the fingers. The 
frequent manual repositioning of the 
drill can cause muscle pulls and other 
injuries because of the weight (over 100 
lb) and awkwardness of the drill-leg 
configuration. 

In conjunction with Bureau efforts to 
devise "quiet" hand-held mining drills, 2 
a lightweight fiberglass feed leg has 
been fabricated. The major advantage of 
fiberglass as the feed leg material is 
that its high strength-to-weight ratio 



results in a lower overall drill weight. 
In fact, the combined weight of a stan- 
dard drill with an aluminum leg is 50 pet 
more than the combined weight of the fi- 
berglass leg and the quiet drill develop- 
ed by the Bureau (table 1). Miner ac- 
ceptance of the quiet drill is increased 
due to the presence of the fiberglass 
feed leg, and the likelihood of injury 
while repositioning the drill is reduced. 
The lighter weight could also lead to an 
increase in miner productivity due to a 
reduction in hole-to-hole repositioning 
time. Another potential but unproven 
benefit of the fiberglass feed leg, even 
when used on standard drills, is a reduc- 
tion in the noise and vibration emanating 
from the feed leg itself. 



^Creare Products, Inc. Development of 
Commercial Quiet Rock Drills. Ongoing 
BuMines contract J01 771 25; for inf., con- 
tact W. W. Aljoe, TPO, Pittsburgh Re- 
search Center, BuMines, Pittsburgh, PA. 

Creare Products, Inc. Development of 
Prototype Quiet Hard Rock Drills. Ongo- 
ing BuMines contract HOI 1 3034; for info., 
contact W. W. Aljoe, TPO, Pittsburgh Re- 
search Center, BuMines, Pittsburgh, PA. 




Another area of consideration for com- 
parison is cost. The greatest difference 
is in the tubing; the inner components 
are similar and are low in cost, so 
they have little effect on the total 
costs. The fiberglass tubing costs are 
considered high because they represent 
small-order pricing, not large-volume 
discounts. The final price at production 
level is arbitrary for the fiberglass 
feed leg because of this and other vari- 
ables, and is reflected as a wide price 
range in table 2. 

TABLE 1. - Comparisons of rock-drill and 
feed-leg weights, pounds 





Bureau'' 


Standard2 


Feed lee» •••••••••••• 


18 
50 


30 


Hard rock drill 


73 


Total 


68 


^103 







^Fiberglass feed leg, "quiet" drill. 
^Aluminum feed leg. 

^51 pet heavier than Bureau feed leg 
drill. 

TABLE 2. - Approximate costs of feed 
legs, dollars 



FIGURE 1. - Standard aluminum feed leg on 
hand-held percussion drill. 





Feed leg 




Fiberglass 


Standard Al 


Tubing cost 

Total cost 

Selling price*" . . 


200 

475 

575-800 


100 

375 

600-700 



^Estimated. 



DESIGN 



The construction of the fiberglass feed 
leg is similar to that of aluminum feed 
legs. Figure 2 shows the individual com- 
ponents of the fiberglass feed leg; the 
drawing in figure 3 shows its overall 
dimensions. The outer fiberglass tube 
provides containment of the pressurized 
air for extension and force. A piston 
with leather seals is connected to the 
inner tube, also made of fiberglass, 
which slides relative to the outer tube. 
Aluminum is used for the piston parts, 
bushings, end cap, and bearing sleeves. 

To provide the thrust required for a 
hard rock drill (over 600 Ibf), a special 



fiberglass-wound tube developed for hy- 
draulic cylinders and pressure vessels 
was selected for the outer and inner 
tubes. These new fiberglass cylinders 
are available in the required dimensions 
"off-the-shelf." A cross-weave fiber- 
glass tube has ultimately been selected 
over a single-weave tube used for prelim- 
inary testing. The newer tube has the 
better flex and strength characteristics 
that are a concern in the rock drilling 
environment, even though the earlier tube 
has performed well under very stressful 
conditions. The material properties of 




FIGURE 2. - Components of fiberglass feed leg. 



Guide bushing cap 



Nut 



Outer tube 



Inner tube with brake 



End cap 



rt'»fl«*>Vl^*'Vi^ 



WW^ 








Stinger 



FIGURE 3. - Overall dimensions of fiberglass feed leg. 



this fiberglass include a high strength- 
to-weight ratio and high internal 
damping, double that of aluminum. Ten- 
sile strength is 65,000 psi, compressive 
strength is 50,000 psi, and the charpy 
impact rating is 5 fflbf,3 Comparable 
aluminum tubing of 2024 alloy has 70,000 
psi tensile strength and a charpy impact 
rating of 3 fflbf. 

A return spring with rate of extension 
brake is also built into the leg. This 
return spring and brake fit inside the 
outer tube to provide a retraction force 
and limit the rate of leg extension. The 



limiting of extension rate is needed as a 
safety feature if the drill steel fails 
or the leg stinger slips, a major hazard 
with these drills. 



■^Charpy impact is a pendulum- type, 
single-blow impact test in which the 
specimen, usually notched, is supported 
at both ends as a simple beam and broken 
by a falling pendulum. The energy ab- 
sorbed, as determined by the subsequent 
rise of the pendulum, is a measure of the 
impact strength or notch toughness. 



TESTING 



To verify the potential value of fiber- 
glass feed legs on both the standard and 
the Bureau devised quiet drills, Tech En- 
terprises, Inc.,'* a small manufacturer of 
hand-held rock drills agreed to design, 
build, and test a prototype for the Bu- 
reau. Tech Enterprises' expertise in 
this area and the initial testing at the 
Colorado School of Mines Experimental 
Mine provided valuable information that 
led to the final design of the leg. Two 
different drill-mounting methods were 
used, an "offset stoper" version (fig. 4) 
and a standard feed leg version (fig. 5). 

^Reference to specific manufacturers 
and materials does not imply endorsement 
by the Bureau of Mines. 



During initial testing, the feed leg 
provided enough thrust (about 200 to 400 
Ibf) to stop drill steel rotation; how- 
ever, several minor modifications were 
made to counteract problems that arose. 
First, the mounting clamps failed and 
slipped on the outer fiberglass tube. To 
eliminate this problem, the outer tubing 
was threaded, and a new mount was design- 
ed to reduce the bearing pressure needed 
to hold the clamps firmly to the tube. 
Second, a Nylatron bearing caused stick- 
ing and scoring inside the leg; an alumi- 
num replacement bearing eliminated this. 
Third, elastomer seals were replaced with 
leather seals because of sticking and 
bonding problems between the elastomer 
and the fiberglass. 





FIGURE 4. - Offset stoper version of fiberglass 
feed leg. 



FIGURE 5. - Standard version of fiberglass 
feed leg. 



In-mine testing showed that the thrust 
capability of the feed leg was unchanged 
after the modifications were made. Im- 
pacts of rocks during drilling and trans- 
port of the drill with feed leg attached 
did not damage the fiberglass surface. 



Further testing is planned with produc- 
tion mines in Canada, South Dakota, Colo- 
rado, and Wyoming that have expressed in- 
terest in the new drill and fiberglass 
feed leg to ensure that the new materials 
will perform over an extended period. 



SUMMARY 



The fiberglass feed leg has performed 
as expected and shows potential as a 
lightweight, highly damped, and lower vi- 
brating alternative to the standard alu- 
minum and steel feed legs; drill opera- 
tors consistently have preferred the 
lightness and balance of the fiberglass 
feed leg. About 80 holes have been 
drilled using the fiberglass feed leg 
with the usual minor problems in proto- 
type equipment being found and 
corrected. 

During early testing for noise attentu- 
ation, comparisons between the fiberglass 
feed leg and an aluminum feed leg indi- 
cated little or no noticeable noise re- 
duction. This can be attributed to the 
much higher noise level of the rock drill 
during operation. While actual use dem- 
onstrated no obvious noise reduction, the 



vibration damping and weight advantages 
support the continued development and use 
of the fiberglass feed leg. 

More testing is required to determine 
compatibility and durability of the fi- 
berglass tubes and aluminum bearing com- 
ponents. A commercial firm plans to man- 
ufacture and test the lightweight. Bureau 
devised quiet rock drills with fiberglass 
feed legs in several mines. Preliminary 
reports indicate the company's willing- 
ness to produce the feed leg for commer- 
cial use when tests are sucessfully com- 
pleted. Although the cost of the proto- 
type fiberglass feed leg was higher than 
that of an aluminum feed leg, the cost of 
the commercial fiberglass feed leg is ex- 
pected to be much lower. 



vSrU.S. CPO: 1985-505-019/20,107 



INT.-BU.OF MIN ES,PGH.,P A. 28)03 



■TIRS? 



*»fifiMnim}ifM"»<i»<'Tni^m!Hiitii!i»T)mir>fTfTr'''"*^'r 



U.S. Department of the Interior 
Bureau of Mines— Prod, and Distr. 
Cochrans Mill Road 
P.O. Box 18070 
Pittsburgh. Pa. 15236 



AN EQUAL OPPORTUNITY EMPLOYER 



OFFICIALBUSINESS 
PENALTY FOR PRIVATE USE. S300 

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